1. Field of the Invention
The present invention relates to apparatus for providing thread forms on a workpiece, and more particularly to threading inserts and chip breakers used therefor. Still more particularly, the present invention relates to a threading insert which is indexable and integrally incorporates a pressed-in chip breaker. Still more particularly, the present invention relates to an indexable threading insert with integral pressed-in chip breaker for providing buttress thread forms on a workpiece, especially of the kind used commonly in the oil patch industry.
2. Description of the Related Art
Threading of a workpiece is conventionally performed using a positive, precision ground flat-face threading insert. The conventional threading insert is presented in a neutral position to the centerline of the workpiece, which requires that the conventional threading insert have a positive clearance angle. This positive geometry limits the number of cutting edges to just one. The conventional threading insert is used in conjunction with an adjoining, separate, inclined surface mechanical chip breaker. The conventional threading insert and mechanical chip breaker are seated in a pocket of a toolholder for providing selected engagement with respect to a workpiece to thereby provide it with threads.
While the conventional threading insert performs its thread cutting function adequately, there yet remains the problem that when the conventional threading insert cutting edge becomes dull or otherwise unacceptable, the threading insert must be replaced with a new or resharpened one.
Conventional mechanical chip breakers are ground in the form of an inclined plane, having a pointed edge adjacent the cutting edge of the threading insert, inclining increasingly with increasing distance from the cutting edge of the threading insert, and terminating in a planar face. The conventional mechanical chip breaker produces very long, razor-like, wiry chips which can damage the threading insert, the toolholder, the workpiece, or the operator. Further, these chips are difficult to collect and pose disposal handling problems.
Still further, the optimum position of the conventional mechanical chip breaker with respect to the cutting edge of the threading insert is almost impossible to consistently achieve. As a result, material build-up between the mechanical chip breaker and the threading insert can be expected to occur. This build-up ultimately can cause poor part finish, premature insert failure, and even possible insert breakage.
It is ideal for the workpiece to be broken into manageable chips in the form of "C's" and "9's" which are narrower than the threads being formed. Narrowing the removed material helps to initiate chip control by bending the material away from the sides of the thread grooves, thereby concentrating the stress and strain properties of the material toward the center of the chips. Thus, the prior art chip breaker suffers from being deficient in chip management.
The ability of pressing a chip breaker form onto a positive threading insert is virtually impossible. When pressing into a positive die cavity, a neutral press land cannot be avoided when the green insert is ejected. A neutral press land prevents the insert from having a sharp edge at the intersection of the relief angle and its rake face. Pressing a positive insert without the appearance of a press land presents a major problem with current manufacturing techniques.
Accordingly, what remains needed in the art is a threading insert which is indexable and provided with an integral chip breaker having ideal chip management characteristics, particularly a threading insert and integral chip breaker for providing buttress thread forms on a workpiece.